1. Field of the Invention
The present invention relates to a digital broadcasting receiving system, and more particularly, to a method in which Maximum Likelihood Sequence Estimation (MLSE) is used for the equalization and the noise elimination of a digital broadcasting.
2. Discussion of the Related Art
In case where a signal is transmitted using sky wave or wire in most of digital transmission systems currently used, a transmission system using Pulse Amplitude Modulation (PAM) or Quadrature Amplitude Modulation (QAM) and an ATSC 8VSB transmission system proposed as American digital TV transmission way, signals reflected from various reflectors are combined and received. Since such reflected components cause the distortion of an original signal, the original signal cannot be obtained only with the received signal. An equalizer is used to compensate for the components (ghost or fading signal) causing the distortion of the transmission signal between a transmitting stage and a receiving stage as described above. The equalizer functions to eliminate the components causing the distortion of the original signal.
The equalizer uses a way in which an error is obtained from a difference between an output value of the equalizer and a decision value decided from the output value of the equalizer to update an equalization coefficient.
FIG. 1 is a block diagram illustrating a construction of a digital broadcasting receiving system using the equalizer.
A demodulator 101 performs Analogue-to-Digital (A/D) conversion and carrier restoration/timing restoration for a Radio Frequency (RF) signal received through an antenna, to convert the RF signal into a digital base band signal and output the converted signal to the equalizer 102.
The equalizer 102 updates a coefficient of a filter of the equalizer depending on an error value fed-back in an error generating unit 103 to compensate for a channel distortion included in the digital base band signal. That is, the equalizer 102 compensates for a variety of fading generated during the time when a signal travels from a transmitter to a receiver. An output of the equalizer 102 is inputted to a channel decoder (not shown) and at the same time, inputted to a slicer 104.
The slicer (or decision unit) 104 uses an 8-level slicer, for example.
That is, the slicer 104 receives the equalized signal and compares an equalized signal level with eight predetermined reference signal levels, to output the closest reference signal level to the equalized signal level, to an error generating unit 103 as a decision value.
The error generating unit 103 obtains a difference between an output signal of the equalizer 102 and a decision signal of the slicer 104 , to use the obtained difference as an error. The error is fed-back to the equalizer 102. The equalizer 102 updates a coefficient of the equalizing filter by using the fed-back error.
At this time, there is a high possibility that the received signal traveling through a heavily distorted channel has a different decision value from a transmitted original signal. In this case, there is a drawback in that in the equalizer using the slicer of FIG. 1, an initial convergent speed is slow, and a tracing performance is degraded.